The garlic can be roasted and stored in the refrigerator up to one day ahead.
Cut off pointed end of garlic bulb; place garlic on a piece of aluminum foil, and drizzle with oil. Fold foil to seal.
Bake at 350° for 1 hour; cool. Squeeze pulp from garlic; set aside.
Cook potatoes in a Dutch oven in boiling salted water to cover 20 to 25 minutes or until tender; drain and place in a large bowl.
Mash potatoes with roasted garlic pulp, cream cheese, and next 5 ingredients in a bowl until smooth. Garnish, if desired.